Re: [HACKERS] [PATCH] Generic type subscripting

út 22. 12. 2020 v 17:57 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Dmitry Dolgov <9erthalion6(at)gmail(dot)com> writes:
> > On Tue, Dec 22, 2020 at 12:19:26PM +0100, Pavel Stehule wrote:
> >> I expect behave like
> >>
> >> update x set test[1] = 10; --> "[10]";
> >> update x set test['1'] = 10; --> "{"1": 10}"
>
> > Yes, I also was thinking about this because such behaviour is more
> > natural.
>
> I continue to feel that this is a fundamentally bad idea that will
> lead to much more pain than benefit. People are going to want to
> know why "test[1.0]" doesn't act like "test[1]". They are going
> to complain because "test[$1]" acts so much differently depending
> on whether they assigned a type to the $1 parameter or not. And
> they are going to bitch because dumping and reloading a rule causes
> it to do something different than it did before --- or at least we'd
> be at horrid risk of that; only if we hide the injected cast-to-text
> doesd the dumped rule look the way it needs to. Even then, the whole
> thing is critically dependent on the fact that integer-type constants
> are written and displayed differently from other constants, so it
> won't scale to any other type that someone might want to treat specially.
> So you're just leading datatype designers down a garden path that will be
> a dead end for many of them.
>
> IMO this isn't actually any saner than your previous iterations
> on the idea.
>

I think so there can be some logic. But json has two kinds of very
different objects - objects and arrays, and we should support both.

can be a good solution based on initial source value?

DECLARE v jsonb;
BEGIN
v := '[]';
v[1] := 10; v[2] := 20; -- v = "[10,20]"
v['a'] := 30; --> should to raise an error
v := '{}';
v[1] := 10; v[2] := 20; -- v = "{"1": 10, "2":20}"
v['a'] := 30; -- v = "{"1": 10, "2":20, "a": 30}"

When the source variable is null, then the default behavior can be the same
like json objects. But it doesn't solve well numeric indexes.

because

v := '[]'
v[1.5] := 100; -- it is nonsense

but
v := '{}'
v[1.5] := 100; -- v = "{"1.5":100}" -- and this can have good benefit, but
"1" and "1.0" are different keys.

But maybe we try to design some that are designed already. Is there some
info about index specification in SQL/JSON?

Regards

Pavel

regards, tom lane
>